What Intense Training Does to Your Blood

Last year, 43-year-old Jay Ashman took a routine blood test the morning after a vigorous leg workout at Kansas City Barbell. A few days later, the former rugby player got a call from his doctor saying two key indicators of kidney function were abnormal.

“I went into panic mode,” he recalls. “I was thinking kidney failure, dialysis, dying early, all kinds of crap.” But additional testing determined his kidneys were normal. Heavy weightlifting had skewed the initial readings.

Abnormal blood-work results are actually a common issue among men who work out hard or compete in extreme events. That’s because most lab reference ranges are based on the general population, not avid exercisers, explains Spencer Nadolsky, D.O., a board-certified family-medicine and obesity physician in Maryland. “You need to look at labs in the context of each patient. Otherwise it can cause a lot of worry or excessive testing.”

There aren’t any stats on how many athletic guys are affected, but more men than ever are exercising harder and harder. The number of half marathons is at an all-time high, more than 4.5 million people complete obstacle-course races annually, and experts say that high-intensity workouts are more popular than ever.

Frequent, intense, or sustained exercise can change your body from the inside out, which can raise red flags on routine blood tests. Here’s what you need to know to protect yourself.

Don't Stress the White Coat

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New research reveals that “white-coat hypertension” — the stress of being in a medical environment — is not benign. It can be indicative of how your BP increases in response to stressful situations.

If you’re among the estimated 30 percent of people whose BP usually spikes when they visit the GP, ask your doctor about wearing an ambulatory 24-hour monitor to record blood pressure throughout the day. This will provide the most accurate assessment.

Don’t forget: The new normal for blood pressure is 120 systolic over 80 diastolic.

If You Lift Weights

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. . . Then Your Creatinine May Be High

Normal range: 0.9 to 1.3 mg/dL

Normal change with strength training: 10 to 20 percent higher

What it is: Creatinine results from the breakdown of creatine phosphate in the muscles. Kidneys filter this waste product from the blood, but if they’re not working properly, it can build up. (This is what happened to Ashman.)

Who’s at risk: Lifters and guys with high muscle mass.

Why it rises: A well-muscled guy will naturally have more creatinine than a skinnier counterpart. Couple this with normal muscle breakdown from exercise (especially heavy weight training) and blood readings can spike. “The more muscle you have, the more it will break down and increase creatinine levels,” says Dr. Nadolsky.

What to do: Tell your doctor if you’ve been lifting hard or packed on muscle since your last visit. If your number is above normal, skip the gym for a week and retest.

When to worry: If levels are consistently high and you have other risk factors for kidney disease (diabetes, high blood pressure, family history), consider a cystatin C test or an ultrasound.

That's Not All, Lifters

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Your White-Blood-Cell Count May Also Be High

Normal range: 4,500 to 11,000 white blood cells per microliter

Normal change with strength training: Increase up to two thirds

What it is: White blood cells are vital to your immune system, fighting viruses and other invaders.

Who’s at risk: Intense exercise stresses the immune system, causing a temporary spike in the white-blood-cell count. Research has revealed that a 35-minute eccentric-based quads workout raises it by around two thirds.

Why it rises: Probably an inflammatory response caused by muscle damage. White blood cells, particularly the first responders, arrive at an injury site to clear cellular debris and aid recovery.

What to do: Tell your doctor if an intense exercise session may be to blame. You won’t have to wait too long to retest. Levels have been shown to return to the pre-exercise baseline within 24 hours.

When to worry: Counts above 17,000 cells per microliter that don’t retreat after an exercise break can signal infection, inflammation, or even leukemia, says Brandee Waite, M.D., at UC Davis Medical Center, especially if you also have fever, chills, persistent fatigue, swollen glands, or easy bruising.

If You Do Crossfit

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. . . Then Your Creatine Kinase May Be High

Normal range: 44 to 196 units/liter

Normal change with exercise: Up to five times the upper limit

What it is: Creatine kinase (CK) is an enzyme that aids muscle-cell function. Levels rise with muscle damage. Doctors often order the test to check for a condition called rhabdomyolysis (or rhabdo), which can be exercise-induced. By-products of muscle breakdown leak into the bloodstream and damage the kidneys.

Who’s at risk: Elevated CK levels are commonly linked to high-intensity programs such as CrossFit, but regular strength training and running can raise them too. You’re also at higher risk once you resume exercise after a hiatus or when trying something new, says Dr. Nadolsky.

Why it rises: Muscle damage from a workout is the usual cause, particularly if you were doing eccentric or “negative” moves like slow lowering from a pullup or bicep curl, or downhill running. This can result in tiny holes in the membranes surrounding muscle fibers, allowing CK to leak out.

What to do: Let your doctor know if heavy WODs may be to blame, and retest after an exercise break. Make sure to give your body enough time to clear excess CK. Research has shown that levels can remain elevated seven days after a weightlifting workout.

If You're a Bodybuilder

. . . Then Your AST and ALT May Be High

Normal change with exercise: Up to double the high end of normal levels

What they are: Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) are generally called liver enzymes. High levels can signal liver disease such as hepatitis.

Who’s at risk: Bodybuilders

Why they rise: These enzymes aren’t just in your liver. Smaller amounts, especially of AST, are also in your muscles, says Dr. Nadolsky. So when they break down due to exercise, you may see a spike.

What to do: Tell your doctor if you’ve been lifting heavy (weights where three reps is challenging). If your numbers are worrisome, take a hiatus for a week or two and retest.

When to worry: Levels more than two times the upper limit are unlikely to stem from exercise, says Dr. Waite. That can indicate liver disease, especially if you also have abdominal pain, digestive difficulties, or yellowing skin.

If You Run

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. . . Then Your Red-Blood-Cell Count May Be High

Normal range: 4.5 million to 5.9 million cells per microliter

Normal change with running: About double the high end of normal

What it is: Red blood cells carry oxygen from the lungs to the rest of your body, and having too few of them can affect the amount of oxygen that reaches your tissues. This test tells you how many you have.

Why it rises: It’s an adaptation to assist your body with the stress of endurance exercise. “Runners’ bodies respond to training by creating more red blood cells to carry oxygen to their muscles,” Dr. Waite explains.

What to do: Red-blood-cell life span is about 120 days, so a recheck after a couple weeks off isn’t likely to make a difference, says Dr. Waite. Either stop running or drop to a very low- intensity level for a month or more to see if it declines.

When to worry: Counts above 11 million cells per microliter could signal bone-marrow issues such as cancer. Specialized blood tests can check cell size and shape.

If You Do Lots of Cardio

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. . . Then Your Total Cholesterol May Be High

Normal range: Under 200 mg/dL

Normal change with cardio: Levels 200 or above, depending on HDL

What it is: Total cholesterol is the sum of “bad” low-density (LDL) and very low-density (VLDL) lipoprotein and “good” high-density (HDL) lipoprotein. High LDL and VLDL cholesterol levels can cause arterial-plaque buildup, raising heart-disease and stroke risk.

Who’s at risk: Athletes, especially cyclists or runners who eat a healthful diet. Their HDL levels can reach 70 mg/dL or more—much greater than the healthy minimum of 40 mg/dL. And you want high HDL, since it helps the liver clear LDL and VLDL.

Why it rises: Exercise may increase production of an enzyme called lecithin-cholesterol acyltransferase, which promotes HDL formation.

What to do: If your total cholesterol is high, ask your doctor for your non-HDL reading, says Dr. Nadolsky. That’s total cholesterol minus HDL, so it’s only the bad stuff. Optimal is less than 130 mg/dL.

When to worry: A non-HDL reading above 130 mg/dL can put you at risk for heart disease, especially if you have high blood pressure or a family history.

If You Cycle

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. . . Then your PSA Levels May Be High

Normal range: Under 4 nanograms per milliliter

Normal change with cycling: Up to 10 percent higher

What they are: Prostate- specific antigen (PSA) is a protein produced by prostate-gland cells. Infections, enlargement, or cancer can elevate its levels.

Who’s at risk: Long-distance cyclists may see a temporary spike in PSA. When Australian researchers tested levels in men 50 and older before and after riding at least 34 miles, they found their PSA was about 10 percent higher afterward.

Why they rise: Thank that hard saddle. “If you have something irritating the prostate, either with pressure from an uncomfortable bike seat or with infection, blood vessels expand, allowing more PSA to leak into your blood,” explains Jamin Brahmbhatt, M.D., a urologist with Orlando Health.

What to do: For an accurate reading, refrain from anything that can irritate the prostate—whether a long bike ride or (sorry) ejaculation—for two days beforehand, Dr. Brahmbhatt recommends.

When to worry: When analyzing your PSA levels, your doctor should be looking for trends rather than one slightly elevated reading, Dr. Brahmbhatt notes. PSA levels that gradually increase over time could indicate cancer, especially if you experience trouble urinating, decreased flow, or pelvic discomfort.

Christa SgobbaFor nearly 10 years, Christa has created health, fitness, nutrition, and wellness content that’s steeped in science but engaging enough that people actually want to read it.

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